ARTHRITIS RELATED TO CRYSTAL DEPOSITION
In gout, hyperuricemia and the deposition of monosodium urate crystals in joints will result in recurrent bouts of acute arthritis. The hyperuricemia can be caused by overproduction or underexcretion of uric acid.
• Primary gout (90%) is idiopathic, affects males more than females, and is typically seen in older men.
• Secondary gout (10%) is seen with excessive cell breakdown (chemotherapy), decreased renal excretion (drugs), and Lesch-Nyhan syndrome.
Gout affects the great toe (podagra, characterized by an exquisitely painful, inflamed big toe), ankle, heel, and wrist.
Joint aspiration shows birefringent, needle-shaped uric acid crystals and numer-ous neutrophils. Tophi are deposits of crystals surrounded by inflammation. Skin ulceration and destruction of adjacent joints may occur. Complications include joint destruction and deformity, uric acid renal calculi, and renal failure. Treatment is NSAIDs, colchicine, probenecid, and allopurinol.
Pseudogout (chondrocalcinosis) is deposition of calcium pyrophosphate crystals in joints, leading to inflammation. Affected patients are usually age >50. The knee joint is most commonly involved. Aspiration of the joint demonstrates positively birefringent (weak), rhomboid-shaped crystals. Pseudogout is associated with many metabolic diseases (e.g., diabetes, hypothyroidism, ochronosis), and it may mimic OA or RA.